The Fourier Transform (FT) is an indispensable mathematical tool for analyzing the spectrum structure of electrical waveforms that has been implemented with hardware and software in connection with various versions of the Fast Fourier Transform (FFT) technique. The use of the FFT in real-time applications has been limited to relatively low data rates by these techniques.
The present invention is related to a signal processing circuit and technique that is useful for carrier frequency and waveform acquisition techniques, clock recovery, tone excision, doppler measurements and to a new method, called the Instantaneous Fourier Transform (IFT), which derives the transform of a preselected band of frequencies by using analog hardware in a feedback configuration. The disclosed implementation uses conventional elements such as mixers, filters, local oscillators, and delay lines.
When IFT is compared with four of the more commonly used prior art transform techniques, it is found that there are advantages associated with this technique.
(1) Compared to a chirp transform or an acousto-optical transform, the IFT provides orders of magnitude better resolution with a much simpler design.
(2) Compared to the Fast Fourier Transformer (FFT), the IFT has faster real-time analysis, and requires no sampling or quantization.
(3) Compared to filter bank methods, the IFT is substantially less expensive and generally will have larger time-bandwidth products.
(4) Compared to the scanning radiometers, the IFT usually will be faster by orders of magnitude.
A few of the possible areas of practical application of the circuit of the present invention are for IFT carrier acquisition, data clock frequency recovery, tone excision, waveform acquisition, and doppler measurements. The band of frequencies that are analyzed in IFT can be shifted, widened, or narrowed in bandwidth by minor adjustments to the parameters.